Commercial fertilizers contain nutrients that are essential for plant growth, with the three main nutrients being nitrogen (N), phosphorus (P), and potassium (K). Commercial fertilizers are highly concentrated and water soluble. When fertilizer is applied to soil, it dissolves in the water present in the soil, and the nutrients are free to react with soil minerals, other chemicals, and micro-organisms.
Nitrogen undergoes microbial transformations in the soil. In its end form, nitrate, it can leach from the soil and/or, by the denitrification process, can volatilize into the atmosphere when conditions are right. Leaching losses can be very detrimental to the environment as nitrates in ground water promote the growth of algae blooms and can cause the oxygen-deprivation condition hypoxia. It is documented that nitrate leaching and run-off in the Mississippi River Basin and Chesapeake Bay drainage contributes to the hypoxia zone in the Gulf of Mexico and Chesapeake Bay. Presently there are many government programs proposed and being implemented to reduce nitrate loading in these and other locations. Improved management of nitrogen in fertilizer and other agricultural contexts is a key target for these efforts and a worldwide priority.
Nitrogen denitrification is also detrimental to the environment. This process occurs when soils are water-saturated and soil micro-organisms metabolize nitrate nitrogen to capture oxygen. Once this occurs, gaseous nitrogen and nitrous oxide gas are released. Nitrous oxide is a powerful greenhouse gas that destroys ozone in the atmosphere.
To prevent and lessen nitrogen loss from fertilizer applications, farmers presently attempt to apply the right amount of fertilizer at the best time of year and place it where it has the least loss potential. Unfortunately, nitrogen soil reactions are very rainfall and temperature dependent. So, despite farmers' best efforts, a significant amount of nitrogen is lost from the cropping system each year.
The most common and popular form of solid nitrogen fertilizer is urea. Urea nitrogen is produced as granules and prills and is subject to the same losses mentioned above, but, in addition, surface-applied urea is subject to volatilization. To lessen the chance of urea volatilization, leaching, and denitrification, different coatings and additives are being applied to urea to slow down its dissolving in the soil, and to interrupt the reactions it undergoes in the soil. Such urea coatings include sulfur, slowly-soluble chemical polymers, and chemicals that interrupt bacterial reactions with urea, such as dicyandiamide (DCD) and the AGROTAIN® brand urease inhibitor offered by Koch Industries (formerly AGROTAIN International, L.L.C.), of St. Louis, Mo.
Because the coatings increase the cost of urea nitrogen, such fertilizers have been used primarily in high-value markets like turf grass, ornamentals, and fruit and vegetable production. With the present emphasis on the environmental impacts of fertilizer nitrogen, however, there is a great deal of interest in using these technologies in grain crop production. One company, Agrium Advanced Technologies of Loveland, Colo., is presently marketing a polymer-coated urea product for grain production systems.
Yet existing coatings and chemical additives for urea do not fully address the crop and environmental needs in managing nitrogen fertilizer. The ideal nitrogen fertilizer would be one that farmers or custom fertilizer applicators could apply when field conditions permit, but would only become available to the crops when needed. Since that time varies, depending on several factors, such as the type of crop grown, stage of crop development, the weather, and planting date, the present technology does not meet farmers' needs.
Other forms of dry nitrogen fertilizer are ammonium nitrate and ammonium sulfate. The nitrogen in these fertilizers undergoes the same chemical conversions in the soil that results in nitrate leaching and denitrification, so using these materials does not solve environmental issues of concern.
Chemically-complex, slowly-available, liquid nitrogen fertilizers are also marketed as controlled-release sources of nitrogen. Like the dry nitrogen fertilizers, the nitrogen availability in these materials is strongly dependent on soil moisture, temperature, and soil microbe activity, and this fertilizer format also does not solve the environmental issues of concern.
Phosphorus in surface waters also is responsible for increase alga growth and also contributes to the hypoxic zones in the Gulf of Mexico and Chesapeake Bay. Agricultural phosphorus enters surface waters primarily through soil erosion and improper manure management. Fertilizer phosphorus is very reactive in soils and can react and form chemical complexes with other minerals in the soil. The rate and extent to which this occurs is very pH dependent. On alkaline soils, fertilizer phosphates quickly react with calcium in the soil and form insoluble calcium phosphate compounds. This greatly reduces the availability and efficiency of phosphate fertilizers. The longer the fertilizer phosphate is in contact with soil, the greater the amount of phosphate that is tied up or fixed in the soil. In highly acid soils, fertilizer phosphate can react with iron and/or aluminum to form insoluble compounds that render the phosphate unavailable to plants. Protecting fertilizer phosphate using slow-release coatings is not presently practiced in agriculture. If the timing of release could be more precisely controlled, such technology would offer great promise in improving phosphate fertilizer use efficiency, as well as affording farmers and custom applicators a great deal of flexibility in when and how the phosphate fertilizer is applied.
With regard to pesticides, their toxicity and environmental fate has long been a concern in agriculture and in general use. In agriculture, the timing of herbicide, insecticide, nematicide, fungicide, and rodenticide applications is very often dependent on when the product can be applied. Weather, soil conditions, development of the crop, life stage of the pest, and timing the application to be effective when the pest is present are all critical factors that affect how and when pesticides are applied and how well they work. If the timing of release of pesticides after application could be precisely controlled, it would offer many advantages over how things are done today. More pesticides would be viable because they would not have to last as long between application and actual need. Also, it would give the applicator a great deal of flexibility as to when and how the material is applied. It would increase the efficacy of the product as well. This would be possible in the soil-applied herbicide, insecticide, nematicide, and rodenticide market. Presently, though, there are no products in the pesticide market that utilize any type of activated release mechanism.
Seed planting and germination normally takes anywhere from three to fourteen days, depending on the seed type, soil temperature, and soil moisture. Farmers time their various plantings to make sure each crop has enough time to mature, and to avoid environmental stress from too much or too little rain, or temperature extremes, during growth and development. Because of weather-related problems or time constraints, it is extremely difficult to plant an entire crop or farm during the ideal time frames. This is especially true for large-acreage farms. If farmers had the option to plant seeds whenever soil conditions allowed, but could control when germination was initiated, it would give them tremendous flexibility in their farming operation. Initiating germination could be a very quick process compared to the overall planting operation. Using seed coatings and having an external source method of breaking or dissolving the coating would offer farmers this flexibility in their operation.
Presently there are polymer coatings for various seeds, but the breakdown of the coatings depends on soil water, temperature, and time. These seeds have not been adopted by many farmers because of the germination variables. Having an activated-release coating for seeds would prove much more useful for farmers.
In short, the problem with present technologies is that the time it takes for fertilizer or pesticide to become available to crops, or for seeds to germinate, is totally dependent on two things most farmers cannot control: soil moisture and temperature.